This invention results from a novel and non-obvious combination of two well known waste products in order to recycle such waste products into a useful non-waste and marketable soil. It should be understood that these two components, while known abstractly, are in real day-to-day experience, subject to different engineering disciplines. My proposed combination goes against actual practice in the field. The combination of the invention is unusual and is not to be expected in the practical work-a-day world.
In one embodiment the invention land farms the two wastes; and in another embodiment the two wastes are used in a new and novel composting method. In each instance an improved product results from the new and novel teaching of the embodiments as disclosed and claimed herein.
Each one of the waste products and the prior art manner of treating such waste products will briefly be described. In order to promote a clear and definite understanding of my invention, I will now describe some terms that are useful for a fuller understanding of my invention.
1. Activated Sewage Sludge
Activated sewage sludge results from raw sewage being treated in standard sewage plants throughout the world. Such activated sewage sludge is defined as an organic fertilizer made from sewage freed from grit and coarse solids and aerated after being inoculated with microorganisms. The resulting organic matter is withdrawn from the treating tanks, filtered with or without the aid of coagulants, dried, ground and screened.
Current technology for treatment and handling of such sludge includes: (1) land fill disposal; (2) composting in static pile systems, windrow systems and in-vessel systems; and (3) direct-application fertilizing of grain-crop fields. Problems and limitations associated with each of these known techniques will now be briefly discussed.
A. Land Fill
Dumping sludge at land fills is the most prevalent method of disposal because land fills are common to most communities. Nationwide, the Regional Water Quality Control Boards are now implementing the Landfill Disposal Criteria (LDC) which restricts land fill disposal of wastes exceeding fifty percent (50%) liquids. This restrictive LDC becomes effective in October 1991, and sewage sludge will no longer be suitable for land fill disposal (Please see Health and Safety Cede Section 25179.5(b)).
B. Composting
Composting activated sewage sludge is one of several approaches available to the management of municipal waste water-laden sludge. It is a biological process that converts sludge into a stable humus that can be applied to the land as a soil conditioner and a low-grade fertilizer. In composting, the sludge (biomass and water) is mixed with approximately a one to three ratio of sludge to a bulking agent such as, for example, wood chips. The mixture promotes oxygenation in any one of several well known manners. Air moving in or out of the mixture and heat, naturally produced or intentionally added, over a period of several days causes the human pathogens to die out. Thereafter the wood chips are removed and a useful humus has been produced.
During the past decade, an increasing number of municipalities have begun to compost their sludge. Approximately 115 sludge composting facilities are operational in the United States. (Please see, for example, the United States Environmental Protection Agency "USEPA" Seminar Publication entitled "Composting of Municipal Sludge", 1985. ). This prior art sludge composting operation is not economically feasible and most such composting activity is an economic burden to the municipalities. What is needed is a new technology as provided by this invention wherein the composting is not only self-supporting but provides a useful product that is economically viable for the municipalities.
C. Fertilizing Fields
Fertilizing grain-crop fields is an acceptable practice for activated sewage sludge disposal and has been practiced for the last twenty years. A limiting factor with farm application is inherent toxic metal concentrations in the sludge. Toxic metals are, by definition, bio-accumulative and thus are highly regulated in agriculture. Regional Water Quality Control Boards typically allow grain-crop field farmers to utilize activated sludge as a one-time application, or following three to four years between applications. (Please see, for example, USEPA "A Practical Technology-Land Application of Sludge", 1983.)
In summary the prior art ways for treating activated sewerage sludge are both costly and limited in application. None of these applications, generally speaking, are economically viable or self-supporting.
2. Hydrocarbon Affected Soil
Hydrocarbon-affected soil is defined as soil which is subjected to a spill or leak of hydrocarbon-based compounds. Typical examples are refineries, service stations having leaking underground fuel tanks and the like. The resulting contaminated soil often represents a risk to the ground water of the area and is required by the regulatory agency to be treated. Current methods for treatment of hydrocarbon-affected soil include (1) incineration; (2) land fill disposal; (3) volatilization; (4) soil ventilation; and (5) bioremediation. Each of these techniques will now be briefly described.
A. Incineration
Incineration of hydrocarbon-affected soils is increasingly popular because the contaminated soil is quickly treated and can be replaced in the ground. The process raises the core-temperature of a soil reactor to the point of thermal destruction of the contamination in the soil. The process is energy-demanding and highly specialized, thus restricting its widespread use.
B. Land Fill
Land fill disposal requires transportation of the hydrocarbon affected soils to an approved and specially designed facility. In urban areas, the land fills are experiencing a crisis for space to dispose of domestic waste and regulators are becoming increasingly reluctant to accept hydrocarbon-affected soils.
C. Volatilization
Volatilization of hydrocarbon-affected soils was common during the past decade. Recent studies of the volatile fraction of petroleum-hydrocarbons suggest that air emissions of aromatic hydrocarbons represents a significant health hazard to the public. Local Air Resource Boards are currently restricting uncontrolled aeration of hydrocarbon-affected soils (Sacramento Air Resource Board, 1986).
D. SOIL VENTILATION
Soil venting is a process of drawing hydrocarbon vapors from the soil through a filtering media, such as granular activated carbon, and transferring the contamination from the soil onto a concentrating filter. The equipment and disposal requirements are specialized for soil venting.
E. Bioremediation
Bioremediation of hydrocarbon-affected soils is a proven technology which results in the complete destruction of the hydrocarbon products to carbon-dioxide and water. Treatability studies show that degradation of light-fraction hydrocarbons (gasoline and aromatic) occurs within two weeks when the micronutrient and moisture contents are optimized. Heavy-faction hydrocarbons (diesel and kerosene) typically degrade within three months.
Bioremediation of hydrocarbon-affected soil is quickly becoming the preferred method of treatment. Micro-nutrients are adjusted in the soil and the natural soil bacteria proliferate and digest the hydrocarbon. Micro-nutrients include; nitrogen, phosphorus, and potassium. Bioremediation is applicable, however, only at a fraction of sites where there is adequate room to create a land farm for a period of a few months.
In summary, there is a desperate and heretofore unsolved need for an improved soil treatment that will increase the yield of useful non-waste balanced soil. This invention fills that need and has the added benefit of recycling two waste products into a beneficial and highly marketable product that is environmentally safe.